The present invention relates to oxymethylene polymer molding compositions. More particularly, the present invention relates to oxymethylene copolymer molding compositions that contain a certain elastomeric polyurethane, and which may be molded into articles having enhanced impact strength properties.
Oxymethylene polymers, having recurring --CH.sub.2 O--units have been known for many years. They may be prepared by the polymerization of anhydrous formaldehyde or by the polymerization of trioxane which is a cyclic trimer of formaldehyde.
The usefulness of oxymethylene polymers in molding compositions has also been known for years. For example, U.S. Pat. No. 3,275,604 discloses a moldable oxymethylene copolymer comprising oxymethylene groups and oxyethylene groups, with said oxyethylene groups having a --CH.sub.2 OR group pendant therefrom, which may be prepared by polymerizing a source of oxymethylene units such as trioxane with a glycidyl ether.
For certain molding applications, e.g., exterior automobile body parts, molding compositions that impart good impact strength to articles molded therefrom are highly desirable. It is not enough, however, that the molded objects exhibit improved impact strengths at room temperature and above, but for many uses they must also retain enhanced impact properties at temperatures as low as -20.degree. F. and lower. For example, low temperature impact retention is especially important when the molded objects are to be used or are frequently present outdoors. Furthermore, it is important that the addition of the impact modifier to the oxymethylene composition not reduce the flexural modulus of the resulting molded articles to unacceptable values. In short, what is needed is an impact modified oxymethylene composition that can be molded into articles that have enhanced impact strengths at both room temperatures and low temperatures (such as -20.degree. F. and lower), and retain commercially useful flexural modulus values.
Accordingly, it is an object of the present invention to provide an oxymethylene polymer molding composition that may be molded into articles which exhibit enhanced impact strength.
It is another object of the present invention to provide an oxymethylene polymer molding composition that may be molded into articles which exhibit enhanced impact strength and which retain enhanced impact strength value at temperatures as low as -20.degree. F.
It is stell another object of the present invention that the articles molded from the impact modified oxymethylene compositon have useful flexural modulue values.
These and other objects, as well as the scope, nature, and utilization of the present invention, will be apparent to those skilled in the art from the following description and appended claims.